Not to mention another package, but there is a nice app call wallp in potato. It will update your wallpaper for you every so often. The easy way to use this or your program is to add a line in .xinitrc in your home directory. If the file does not exist, make it so it looks like:
exec <some image program> & <your window manager> anything added here is run when X starts. The last program in the list does not have a '&' at the end and when it closes, X stops.
